TL;DR – with potentially a billion year headstart on evolution, where the hell are all the s?
The Fermi paradox or Fermi’s paradox, named after Enrico Fermi, is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations, such as in the Drake equation, and the lack of evidence for such civilizations. The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are:
There are billions of stars in the galaxy that are similar to the Sun including many billions of years older than Earth.
With high probability, some of these stars will have Earth-like planets, and if the Earth is typical, some might develop intelligent life.
Some of these civilizations might develop interstellar travel, a step the Earth is investigating now.
Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in about a million years.
According to this line of thinking, the Earth should have already been visited by extraterrestrial aliens. In an informal conversation, Fermi noted no convincing evidence of this, nor any signs of alien intelligence anywhere in the observable universe, leading him to ask, “Where is everybody?”
This is a damn compelling argument, in the same way that the lack of evidence of any time travellers is clear evidence that time travel is not possible… given an infinite amount of time ahead of us.
So what happened – The Great Filter maybe?
With no evidence of intelligent life other than ourselves, it appears that the process of starting with a star and ending with “advanced explosive lasting life” must be unlikely. This implies that at least one step in this process must be improbable. Hanson’s list, while incomplete, describes the following nine steps in an “evolutionary path” that results in the colonization of the observable universe:
- The right star system (including organics and potentially habitable planets)
- Reproductive molecules (e.g., RNA)
- Simple (prokaryotic) single-cell life
- Complex (eukaryotic) single-cell life
- Sexual reproduction
- Multi-cell life
- Tool-using animals with big brains
- Where we are now
- Colonization explosion.
According to the Great Filter hypothesis, at least one of these steps must be improbable.
I liked Wait But Why’s take on this a lot, which covers three possibilities:
1) We Are rare
2) We Are st
3) We Are Fucked
So what say you: why are we so alone in the (observable) universe? I grant you that what we can observe is appallingly tiny given the unimaginable scale of the universe, so “what we can observe” may just not be enough by many orders of magnitude.
I have my own ideas, but I’d like to hear what other mutants think.